(1) Field of the Invention
This invention relates to a leaf spring, more specifically to a leaf spring having its width and sectional area substantially fixed in every position along its longitudinal direction.
(2) Description of the Prior Art
Conventionally, leaf springs used in car suspension systems, etc., are chiefly made of steel. To provide lighter leaf springs, however, steel as the material for the springs is being replaced by FRP (fiber reinforced plastic). In a prior art steel leaf spring, which has fixed Young's modulus throughout the length thereof, the sectional configuration can be varied according to the position to ensure uniform stress distribution without causing any confusion in design.
For uniform stress distribution, even a FRP leaf spring needs to have its sectional configuration varied according to the position by, for example, tapering. In a method for continuously manufacturing FRP leaf springs by continuously extruding a mixture of fibers and resin, which is highest in mass-producing capability, it is necessary to repeat continuously the increase and decrease of the amount of fibers and resin used in order to vary the sectional configuration as aforesaid. In such continuous production, however, the fibers used are continuous, so that it is impossible or very difficult to repeat the increase and decrease of the amount of fibers continuously. Even if only the amount of resin is to be varied, the fixed amount of fibers used will set limits to the variation of the amount of resin used. Moreover, the amount of heat produced by a heating device need be continuously varied according to the amount of resin. In any case, the construction of the device, as well as the control thereof, will be complicated in some measure. Even though only the amount of fibers can be varied, the Young's modulus of the leaf spring will fail to be fixed throughout its length unless the fiber content is fixed in every position along the length. Accordingly, the design calculation cannot help being complicated.
With the sectional area kept fixed, the leaf spring, like a corvette type leaf spring as shown in FIG. 14, will be changed in width as its thickness is changed. If the end portion of the spring is thinned, then the width thereof will be increased to enlarge the components of the suspension system, thereby prohibiting the mounting thereof or causing interference with a tire chain or the like to constitute a hindrance to uniform stress distribution (see FIG. 14).